Cerclage is a known fixation technique in which a bone is encircled by a flexible member such as a cable which is drawn tight and clamped. This may serve to hold portions of bone or bone graft together and/or to retain some surgically applied component. For an account of current cable techniques for trochanteric reattachment, femoral allograft fixation and fractures of the proximal femur in revision total hip arthroplasty, the reader is referred to D. M. Dall, Techniques in Orthop. 1991; 6(3):7-16. This describes, among other things, use of a bone fastener for the greater trochanter, as disclosed in U.S. Pat. No. 4,269,180. This known bone fastener is a generally H-shaped implant comprising a base structure including a pair of limbs joined by a bridge, the bridge being bounded by a front face, a rear face and edge faces, a plurality of teeth protruding from the base structure, all the teeth lying on the same side of the base structure, and at least one hole in the base structure for receiving a cable, the hole being elongate in form, extending lengthways through the bridge, and being open at each end. The bridge is adapted to be crimped so that cable(s) can be passed through the hole(s), pulled tight, and then locked by crimping.
FIG. 1 is a drawing, taken from the cited paper, showing a femur 10 that has undergone reconstructive surgery including use of a fastener 12 according to U.S. Pat. No. 4,269,180. In this procedure, the greater trochanter 16 was cut (osteotomised) to facilitate installation in the bone cavity of an internal bone graft 14 and the stem of a prosthesis (not shown but corresponding to stem 71 in FIG. 7). Thereafter the greater trochanter 16 was reattached to the femur 10 by means of the fastener 12 and cerclage cables 18. In addition a fracture 20 of the femur was surgically treated with a further application of cerclage techniques. Thus elongate medial and lateral bone grafts 22 have been applied to the bone, and bound in place by a multiplicity of cerclage cables 25, each of which has been drawn tight and had its ends locked by crimping in an individual crimp sleeve 26.
A disadvantage of cerclage fixation is that it tends to provide relatively little resistance to some forms of displacement, e.g. relative rotation of components and/or portions of bone and/or bone grafts encircled by cerclage cables. Furthermore some shapes and locations are not well suited to cerclage. A second technique involves screws, which are screwed into bone. A screwed connection is commonly quite good at resisting relative displacement such as rotation. But particularly where the bone is weak, e.g. being spongy, a screwed connection will be of low mechanical strength. Furthermore, if screwing were to be substituted for cerclage for securing the bone grafts 22 shown in FIG. 1, there would be a problem in the upper region, in that only short screws could be used since otherwise they would meet the stem which is typically of metal. Thus cerclage and screw fixation each have advantages and disadvantages, and it would be desirable to have a system that made the advantages of both available.